1. Field of the Invention
The present invention relates to a magnetic field sensing element whose electrical resistance changes in relation to the direction of magnetization of a free magnetic layer that is affected by both the direction of pinned magnetization of a pinned magnetic layer and an external magnetic field. The present invention more particularly relates to a method for manufacturing a magnetic field sensing element that is able to increase a longitudinal bias magnetic field and allows magnetization of the free magnetic layer to align in a direction for appropriately intersecting magnetization of the free magnetic layer.
2. Description of the Related Art
A magnetoresistive magnetic field sensing element is categorized as an AMR (Anisotropic Magnetoresistive) head when it includes an element that exhibits a magnetoresistive effect, and a GMR (Giant Magnetoresistive) head when it includes an element that exhibits a giant magnetoresistive effect. The AMR head has a monolayer structure in which the element exhibiting the magnetoresistive effect is composed of a magnetic material. The GMR head has, on the other hand, is a multilayer structure in which the element includes a plurality of laminated materials. While the giant magetoresistance effect can be generated by several different structures, a spin-valve type thin film magnetic element is commonly used because it has a high rate of change of magnetoresistivity against a weak external magnetic field.
FIG. 15 is a cross sectional view of our exemplary conventional spin-valve type thin film magnetic element as seen from the side facing a recording medium.
The spin-valve type thin film magnetic element shown in FIG. 15 is a so-called bottom type single spin-valve type thin film magnetic element that includes one layer each of an antiferromagnetic layer, pinned magnetic layer, non-magnetic layer and free magnetic layer.
The spin-valve type thin film magnetic element shown in FIG. 15 is composed of, from the bottom to the top, an underlayer 6, an antiferromagnetic layer 1, a pinned magnetic layer 2, a non-magnetic layer 3, a multilayer film 9 composed of a free magnetic layer 4 and protective layer 7, a pair of hard bias layers (permanent magnetic layers) 5 formed on both side faces of the multilayer film 9, and a pair of electrode layers 8 formed on hard bias layers 5. A track width Tw is determined by the width on the surface of the multilayer film 9.
Usually, a Fexe2x80x94Mn or Nixe2x80x94Mn alloy film is used for the antiferromagnetic layer 1, a Nixe2x80x94Fe alloy film is used for the pinned magnetic layer 2 and free magnetic layer 4, a Cu film is used for the non-magnetic layer 3, a Coxe2x80x94Pt film is used for the hard bias layers 5, a Cr or W film is used for the electrode layers 8, and a Ta film is used for the underlayer 6 and protective layer 7.
As shown in FIG. 15, the pinned magnetic layer 2 is magnetized as a single magnetic domain in the Y-direction (the direction of a leak magnetic field from a recording medium: height direction) by an exchange coupling magnetic field with the antiferromagnetic layer 1, and magnetization of the free magnetic layer 4 is aligned in the X-direction (track width direction) under the affect of the bias magnetic field from the hard bias layers 5.
In other words, magnetization of the pinned magnetic layer 2 and magnetization of the free magnetic layer 4 are adjusted to be approximately perpendicular to each other.
A sense current flows from the electrode layers 8 to the pinned magnetic layer 2, non-magnetic layer 3 and free magnetic layer 4 in this spin-valve type thin film magnetic element. The direction of magnetization of the free magnetic layer 4 changes from the X-direction to the Y-direction when the leaking magnetic field from the recording medium is applied in the Y-direction. Electrical resistance changes in relation to the variation of the magnetization direction in the free magnetic layer 4 and the direction of pinned magnetization of the pinned magnetic layer 2 (referred to as a magnetoresistive effect). The leaking magnetic field from the recording medium is sensed by voltage changes based on this changes of electrical resistance.
The spin-valve type thin film magnetic element as shown in FIG. 15 is however, incompatible with high density recording. While magnetization of the pinned magnetic layer 2 is fixed in the Y-direction as a single magnetic domain, as described above, the hard bias layers 5, magnetized in the X-direction, are provided at both sides of the pinned magnetic layer 2. Consequently, magnetization at each side edge of the pinned magnetic layer 2 is particularly affected by the bias magnetic field from the hard bias layers 5, thereby making it difficult to fix the direction of magnetization in the Y-direction.
Accordingly, the direction of magnetization of the free magnetic layer 4, being in a single magnetic domain state by the influence of magnetization of the hard bias layers 5 in the X-direction, and the direction of magnetization of the pinned magnetic layer 2 is not perpendicular in the vicinity of the side edges of the multilayer film 9. Furthermore, magnetization in the vicinity of the side edges of the free magnetic layer 4 is fixed by the strong magnetization from the hard bias layers 5 and is likely to be insensitive to the external magnetic field. As a result, a dead zone having a poor regenerative sensitivity is formed in the vicinity of the side edges of the multilayer film 9.
Although the central portion of the multilayer film 9 substantially contributes to regeneration of the recording medium so as to serve as a sensitive zone manifesting the magnetoresistive effect (a practical track width), it has been difficult to accurately determine the width of the sensitive zone due to irregularity of the dead zone. Therefore, it also becomes difficult to properly comply with narrowing of the track width for high density recording that will be required in the near future.
FIG. 16 shows an improved spin-valve type thin film magnetic element provided for solving the foregoing problems. FIG. 16 also shows a manufacturing process thereof. The same reference numerals as in FIG. 15 denote the same layers.
A part of each side 4a of the free magnetic layer 4 is removed in this spin-valve type thin film magnetic element, and an ferromagnetic layer 13 is formed at each removed part. Second antiferromagnetic layers 10, and electrodes 8 are continuously deposited on the ferromagnetic layers 13 using a lift-off resist 12. The second antiferromagnetic layer 10 is made of an antiferromagnetic material. The ferromagnetic layer 13 is made of, for example, a NiFe alloy film.
In the spin-valve type thin film magnetic element shown in FIG. 16, a longitudinal bias magnetic field is applied by a so-called exchange bias method. An exchange coupling magnetic field is generated between the second antiferromagnetic layer 10 and ferromagnetic layer 13 by the exchange bias method. Accordingly, the longitudinal bias magnetic field in the X-direction is applied to the free magnetic layer 4 by a ferromagnetic coupling between the ferromagnetic layer 13 and free magnetic layer 4.
Use of the exchange bias method can eliminate the dead zone as seen in the spin-valve type thin film magnetic element shown in FIG. 15. Accordingly, the track width can be accurately and easily determined for high density recording that will be required in the near future.
The spin-valve type thin film magnetic element as shown in FIG. 16, however, also has the following problems. Since the tip portions 10a and 10a of the second antiferromagnetic layers 10, deposited by using the lift-off resist layer 12, are tapered, as shown in FIG. 16, the exchange coupling magnetic field generated between each tip portion 10a and ferromagnetic layer 13 becomes extremely small. Particularly, the exchange coupling magnetic field is not generated at all when the thickness of the tip portion 10a is smaller than 50 xc3x85. Accordingly, a sufficient longitudinal bias magnetic field is not supplied to the free magnetic layer 4 in the region located under the tapered tip portion 10a. Thus, the free magnetic layer 4 lying under the track width Tw can only be put into the single magnetic domain state owing to the weak bias magnetic field, causing with great difficulty the generation of Barkhausen noise. In addition, magnetization at each side edge of the free magnetic layer 4, formed under the tip portion 10a, is readily fluctuated since it is not strongly pinned in the track width direction, thereby arising a side-reading problem.
In the method for controlling magnetization of the free magnetic layer 4 by the exchange bias method, the exchange coupling magnetic field is generated in two steps. First, an exchange coupling magnetic field is generated between the first antiferromagnetic layer 1 and pinned magnetic layer 2 and, second, another exchange coupling magnetic field is generated between the second antiferromagnetic layer 10 and ferromagnetic layer 13. Consequently, magnetization of the pinned magnetic layer 2 and magnetization of the free magnetic layer 4 cannot be directed so as to intersect with each other, unless the heat treatment temperature, and the magnitude and direction of the applied magnetic field are properly adjusted.
Accordingly, it is an object of the present invention to provide a method for manufacturing a magnetic field sensing element that is able to generate a large longitudinal bias magnetic field by eliminating tapered tip portions of the second antiferromagnetic layer, so as to properly direct magnetization of the free magnetic layer and magnetization of the pinned magnetic layer in a direction to intersect with each other.
Accordingly, the present invention provides a method for manufacturing a magnetic field sensing element comprising the following steps.
(a) A laminate is formed by sequentially laminating a first antiferromagnetic layer, a pinned magnetic layer, a non-magnetic layer, a free magnetic layer comprising a first free magnetic layer, a non-magnetic intermediate layer and a second free-magnetic layer laminated in this order from the bottom, and a second antiferromagnetic layer.
(b) An exchange coupling magnetic field is generated between the first and second antiferromagnetic layers by applying a heat treatment at a first heat treatment temperature, while applying a first magnetic field to the laminate in the direction perpendicular to a track width direction. As a result, the direction of magnetization of the pinned magnetic layer and the direction of magnetization of the free magnetic layer are fixed in the perpendicular direction with each other, while allowing the exchange coupling magnetic field of the first antiferromagnetic layer to be larger than the exchange coupling magnetic field of the second antiferromagnetic layer.
(c) The element is heat treated at a second heat treatment temperature higher than the first heat treatment temperature, while applying, a second magnetic field in the track width direction, that is larger than the exchange coupling magnetic field of the second antiferromagnetic layer in step (b), and smaller than the exchange coupling magnetic field of the first antiferromagnetic layer. As a result, the free magnetic layer is endowed with a longitudinal bias magnetic field in a direction that intersects the direction of magnetization of the pinned magnetic layer.
(d) A pair of electrode layers are formed on the laminate at a given distance apart from each other.
(e) Finally, the laminate, exposed between a pair of the electrodes, is removed up to midway of the second free magnetic layer.
In the present invention a so-called ferrimagnetic structure is formed by inserting the non-magnetic intermediate layer between the two free magnetic layers in step (a). The ferrimagnetic structure comprises antiparallel orientations of magnetization of the first free magnetic layer and second free magnetic layer. The magnetization may be made more stabilized by forming the ferrimagnetic structure.
According to the method described above, a portion of the second antiferromagnetic layer not covered with the electrode layer, as well as a part of the free magnetic layer, are removed using the electrode formed in the step (d) as a mask. This manufacturing method permits the tip portion of the second antiferromagnetic layer to be less tapered as compared with an antiferromagnetic layer manufactured by the conventional method. Further, by forming the free magnetic layer as a ferromagnetic structure, a sufficient longitudinal bias magnetic field to be supplied from the second antiferromagnetic layer to the free magnetic layer. Consequently, the free magnetic layer can be properly put into a single magnetic domain state to suppress side reading.
According to the present invention, the track width may be narrowed, while facilitating the single magnetic domain structure of the free magnetic layer in response to the high density recording expected in the near future. Furthermore, a magnetic field sensing element is provided that is able to properly suppress Barkhausen noise.
The directions of magnetization of the free magnetic layer and pinned magnetic layer can be adjusted so as to intersect with each other by methods (b) and (c) in the present invention.
In step (b), an exchange coupling magnetic field is generated in the first antiferromagnetic layer and second antiferromagnetic layer by applying a heat treatment at a first heat treatment temperature, in order to fix the directions of magnetization of the first antiferromagnetic layer and second antiferromagnetic layer in the direction of a first applied magnetic field applied (the height direction). The magnitude of the exchange coupling magnetic field of the first antiferromagnetic layer is adjusted to be higher than the exchange coupling magnetic field of the second antiferromagnetic layer. This relation between the intensities described above can be attained by forming a so-called bottom type spin-valve type thin film magnetic element structure in which the first antiferromagnetic layer is formed under the second antiferromagnetic layer, or by appropriately adjusting the composition ratio of the first antiferromagnetic layer.
In step (c), a second magnetic field, which is larger than the exchange coupling magnetic field of the second antiferromagnetic layer in step (b) and smaller than the exchange coupling magnetic field of the first antiferromagnetic layer, is applied in the track width direction. The heat treatment temperature (the second heat treatment temperature) is adjusted to be higher than the first heat treatment temperature.
Magnetization of the pinned magnetic layer is not changed in this step, because the magnitude of the second magnetic field is smaller than the exchange coupling magnetic field of the first antiferromagnetic layer in step (b), and remains to be fixed in the direction (height direction) perpendicular to the track width direction.
Magnetization of the free magnetic layer fluctuates, on the other hand, in the track width direction with the direction of the applied magnetic field, since the magnitude of the second magnetic field is larger than the exchange coupling magnetic field of the second antiferromagnetic layer in step (b). Magnetization of the free magnetic layer is properly aligned in the track width direction due to the generated exchange coupling magnetic field from the second antiferromagnetic layer that is larger than that generated in step (b) as a result of a higher heat treatment temperature than the first heat treatment temperature.
According to the method for manufacturing the magnetic field sensing element in the present invention, the tip portion of the second antiferromagnetic layer is less tapered than the conventional ones, and a large longitudinal bias magnetic field is supplied to the free magnetic layer by forming the free magnetic layer to have a ferrimagnetic structure to facilitate the single magnetic domain structure of the free magnetic layer, thereby enabling magnetization of the free magnetic layer to be adjusted to properly intersect magnetization of the pinned magnetic layer.
The spin-valve type thin film magnetic element is manufactured by forming a laminate comprising the first antiferromagnetic layer, pinned magnetic layer, non-magnetic layer, free magnetic layer and second antiferromagnetic layer on a substrate, followed by heat treating the laminate. Therefore, the surface of each layer formed between the substrate and second antiferromagnetic layer never contacts ambient air when forming the laminate. Accordingly, cleaning by ion milling and inverse sputtering of a surface is not required, as is the case when the surface contacts ambient air. Accordingly, the magnetic field sensing element can be easily manufactured with good reproducibility. Furthermore, eliminating the need of cleaning of the surface of each layer by ion milling or inverse sputtering provides an excellent manufacturing method free from troubles arising from the cleaning process, such as contamination by re-adsorption, and adverse effects on generation of the exchange coupling magnetic field due to distortion of surface crystallinity.
A pair of the electrodes to be formed in step (d) may be formed on the second antiferromagnetic layer in step (a), and step (e) may be applied next to step (c) in the present invention.
It is preferable in the present invention to form the electrodes using a lift-off resist layer. The magnetic field sensing element compatible with narrowing the track width for high density recording may be manufactured by properly adjusting the dimension of the track width formed on the lower face of the lift-off resist layer.
The laminate may be removed up to midway of the non-magnetic layer in step (e) in the present invention. Eliminating the laminate permits a large longitudinal bias magnetic field to be applied to the free magnetic layer having a ferrimagnetic structure located under the second ferromagnetic layer to allow the free magnetic layer to be in a single magnetic domain state. In addition, the non-magnetic intermediate layer serves as a back layer, and can acquire large xcex94MR (magnetoresistivity), enabling a magnetic field sensing element to be compatible with the high density recording expected in the near future.
The first antiferromagnetic layer and the second antiferromagnetic layer are preferably formed using an antiferromagnetic material containing Mn and at least one element comprising Pt, Pd, Rh, Ru, Ir, Os, Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr in the present invention.
In the present invention, a CoFeNi alloy is used for at least one and, preferably, both the first and second free magnetic layers in order to improve the material for the first and second free magnetic layers, and to increase an antiparallel coupling force between the first and second free magnetic layers. Consequently, the side edges of the first and second free magnetic layers, located at both sides in the track width direction, are prevented from fluctuating against the external magnetic field. This properly suppresses side-reading through a synergetic effect of an exchange coupling magnetic field acting between the first antiferromagnetic layer and second free magnetic layer. Including Co in the CoFeNi alloy enhances the antiparallel coupling force.
When the laminate comprises a film lamination structure of non-magnetic layer/first free magnetic layer/non-magnetic intermediate layer/second free magnetic layer, the CoFeNi alloy preferably comprises about 9 at % to about 17 at % of Fe and about 0.5 at % to about 10 at % of Ni, with a balance of Co. It is preferred that the Fe content not be larger than about 17 at %, since magnetic distortion becomes larger than xe2x88x923xc3x9710xe2x88x926 and soft magnetic properties are deteriorated. It is also preferred that the Fe content not be less than about 9 at % since magnetic distortion becomes larger than 3xc3x9710xe2x88x926, which also causes deterioration of the soft magnetic properties. It is also preferred that the Ni content not be larger than about 10 at %, since magnetic distortion becomes larger than 3xc3x9710xe2x88x926, while causing decrease of magnetoresistance (xcex94R) and magnetoresistivity (xcex94R/R) due to diffusion of Ni between the non-magnetic layer and free magnetic layers.
It is preferred that the Ni content not be smaller than about 0.5 at % since the magnetic distortion shifts to the negative side from xe2x88x923xc3x9710xe2x88x926.
A coercive force of 790 (A/m) or less may be obtained within the composition range described above.
When the laminate film comprises non-magnetic layer/intermediate layer (a CoFe alloy)/first free magnetic layer/non-magnetic intermediate layer/free magnetic layer, it is also preferable in the present invention that the CoFeNi alloy comprises about 7 at % to about 15 at % of Fe, and about 5 at % to about 15 at % of Ni with a balance of Co. It is preferred that the Fe content not be larger than about 15 at % since magnetic distortion shifts to negative side from xe2x88x923xc3x9710xe2x88x926 to deteriorate soft magnetic properties. It is also preferred that the Fe content not be smaller than about 7 at % since magnetic distortion becomes larger than 3xc3x9710xe2x88x926, which causes deterioration of the soft magnetic properties. It is also preferred that the Ni content not be larger than about 15 at % since magnetic distortion becomes larger than 3xc3x9710xe2x88x926. It is also preferred that the Ni content not be smaller than about 5 at % since magnetic distortion shifts to negative side from xe2x88x923xc3x9710xe2x88x926.
A coercive force of about 790 (A/m) or less may be obtained within the composition range described above.
The Fe content is slightly decreased and Ni content is slightly increased in the CoFeNi alloy as compared with the film construction in which the intermediate layer is not inserted between the first free magnetic layer and non-magnetic layer, since the intermediate layer comprising CoFe or Co has negative magnetic distortion.
The film construction in which the intermediate layer comprising CoFe alloy or Co is inserted between the non-magnetic layer and first free magnetic layer is preferable since diffusion of metallic element between the first free magnetic layer and non-magnetic layer can be more effectively prevented.
It is preferable in the present invention that both the first and second free magnetic layers are formed of the CoFeNi alloy.
The heat treatment temperature in steps (b) and (c), and the preferable composition ranges of the first and second antiferromagnetic layers will be described hereinafter.
In the present invention the first heat treatment temperature is about 220xc2x0 C. to about 245xc2x0 C., and the second treatment temperature is preferably about 250xc2x0 C. to about 270xc2x0 C.
In the present invention, m, representing the composition ratio, is preferably in the range of about 46 at %xe2x89xa6mxe2x89xa6about 53.5 at %, when the antiferromagnetic layer comprises an alloy represented by XmMn100-m, where X in the formula is at least one element from the group Pt, Pd, Ir, Rh, Ru and Os.
It is preferred that the composition ratio m not be less than about 46 at % or more than about 53.5 at %, since the exchange coupling magnetic field becomes smaller than 1.58xc3x97104 A/m even after the first heat treatment at a heat treatment temperature of about 245xc2x0 C. This is because the crystal lattice of the X-Mn alloy is hardly arranged as a L10 type ordered lattice and will fail in manifesting antiferromagnetic properties, or will fail in generating a unidirectional exchange coupling magnetic field.
An exchange coupling magnetic field of about 3.16xc3x97104 A/m may be obtained after the second heat treatment at a heat treatment temperature of about 270xc2x0 C. in the composition range as described above.
The preferable composition ratio m of the X-Mn alloy is within the range of about 48.5 at % to about 52.7 at %, because in this composition range, an exchange coupling magnetic field of more than about 4.74xc3x97104 A/m may be obtained after the first heat treatment at a heat treatment temperature of about 245xc2x0 C.
In one embodiment, the antiferromagnetic layer of the bottom type spin-valve type thin film magnetic element is represented by PtmMn100-m-nZn, where Z is at least one element from the group of Pd, Ir, Rh, Ru and Os. The subscripts m and n indicate the composition ratio and are preferably in the range of about 46 at %xe2x89xa6m+nxe2x89xa6about 53.5 at % and about 0.2 at %xe2x89xa6nxe2x89xa6about 40 at %. In this composition range, an exchange coupling magnetic field of about 1.58xc3x97104 A/m may be obtained by the first heat treatment at a heat treatment temperature of about 245xc2x0 C. The preferable range of the composition ratio m+n is about 48.5 at % to about 52.7 at %.
It is preferred that n not be less than about 0.2 at % since ordering of the crystal lattice of the antiferromagnetic layer is not enhanced, or an effect for increasing the exchange coupling magnetic field is not fully exhibited. It is also preferred that n not exceeding about 40 at % because the exchange coupling magnetic field decreases.
In another embodiment, the antiferromagnetic layer of the bottom type spin-valve type thin film magnetic element is represented by PtqMn100-q-jLj, where L is at least one element from the group of Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr. The subscripts q and j represent the composition ratios are preferably in the ranges of about 46 at %xe2x89xa6q+jxe2x89xa6about 53.5 at % and about 0.2 at %xe2x89xa6jxe2x89xa6about 10 at %.
It is preferred that the ratio q+j not be less than about 46 at % nor more than about 53.5 at %, since the exchange coupling magnetic field becomes 1.58xc3x97104 A/m or less even after the first heat treatment at a heat treatment temperature of about 245xc2x0 C. More preferably the range of q+j is 48.5 at % to about 52.7.
It is preferred that j not be less than about 0.2 at % because the uniaxial exchange magnetic coupling magnetic field is not fully manifested by adding the element L, while if the ratio j exceeds about 10 at % the uniaxial exchange magnetic coupling magnetic field decreases.
When the antiferromagnetic layer of the top type spin-valve type thin film magnetic element includes an alloy represented by XmMn100-m, where X is at least one element from the group of Pt, Pd, Ir, Rh, Ru and Os)m representing the composition ratio and is preferably in the range of about 49 at %xe2x89xa6mxe2x89xa6about 55.5 at %.
It is preferred that m not be less than about 49 at % nor more than about 55.5 at %, since the exchange coupling magnetic field becomes 1.58xc3x97104 A/m even after the second heat treatment at a second heat treatment temperature of about 270xc2x0 C. This is because the crystal lattice of the X-Mn alloy is not arranged as a L10 type ordered lattice will fail in exhibiting antiferromagnetic properties, or will fail in manifesting the uniaxial exchange coupling magnetic field.
It is evident that the antiferromagnetic layer of the top type spin-valve type thin film magnetic element has a lower exchange coupling magnetic field than the antiferromagnetic layer of the bottom type spin-valve type thin film magnetic element in either composition ratio in the range described above, when the element is heat treated, for example, at about 245xc2x0 C. In other words, the exchange coupling magnetic field of the antiferromagnetic layer of the bottom type element can be made higher than that of the antiferromagnetic field of the top type element even after the first heat treatment.
The more preferable range of the ratio m is about 49.5 at % to about 54.5 at %, because an exchange coupling magnetic field about of 3.16xc3x97104 A/m can be obtained by a heat treatment at about 270xc2x0 C. The exchange coupling magnetic field of the antiferromagnetic layer of the bottom type element becomes larger than that of the antiferromagnetic layer of the top type element by applying a heat treatment at about 245xc2x0 C.
In one embodiment, the antiferromagnetic layer of the top type spin-valve type thin film magnetic element is represented by PtmMn100-m-nZn, where z is at least one element from the group of Pd, Ir, Rh, Ru and Os and m and n, representing the composition ratios, are preferably in the range of about 49 at %xe2x89xa6m+nxe2x89xa6about 55.5 at % and about 0.2 at %xe2x89xa6nxe2x89xa6about 40 at %.
It is preferred that the composition ratio m+n not exceed about 55.5 at % since the exchange coupling magnetic field becomes 1.58xc3x97104 A/m or less. More preferably the ratio m+n is about 49.5 at % to about 54.5 at %.
It is also preferred that the ratio n not be less than about 0.2 at %, since ordering the crystal lattice of the antiferromagnetic field is not enhanced, or increasing the exchange coupling magnetic field is not fully manifested. It is also preferred that the ratio n not exceed about 40 at %, because the exchange coupling magnetic field decreases.
In another embodiment, the antiferromagnetic layer of the top type spin-valve type thin film magnetic element is represented by PtqMn100-q-jLj, where L is at least one element from the group Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr. The subscripts q and j represent the composition ratio and are preferably in the ranges of about 49 at %xe2x89xa6q+jxe2x89xa6about 55.5 at % and about 0.2 at %xe2x89xa6jxe2x89xa6about 10 at %.
It is preferred that the ratio q+j not be less than about 49 at % nor more than about 55.5 at % since the exchange coupling magnetic field becomes 1.58xc3x97104 A/m or less even by applying the second heat treatment at a heat treatment temperature of about 270xc2x0 C. The preferable range of q+j is about 49.5 at % to about 54.5 at %.
It is also preferred that the ratio j not be less than about 0.2 at % since the uniaxial exchange coupling magnetic field is not sufficiently improved. It is further preferred that the ratio j not exceed about 10 at % since the uniaxial exchange coupling magnetic field decreases.
The composition of the first antiferromagnetic layer may be the same as the composition of the second antiferromagnetic layer in the present invention. Such antiferromagnetic layers preferably have the following composition ratio.
In one embodiment, the first and second antiferromagnetic layers comprise an alloy represented by XmMn100-m, where X is at least one element from the group of Pt, Pd, Ir, Rh, Ru and Os. The subscript m represents the composition ratio of each of the first and second antiferromagnetic layers and is preferably in the range of about 49 at %xe2x89xa6mxe2x89xa6about 53.5 at %.
Consequently, the exchange coupling magnetic field of the first antiferromagnetic layer can be made as large as about 1.58xc3x97104 A/m, or more, while allowing the exchange coupling magnetic field of the first antiferromagnetic layer to be larger than the exchange coupling magnetic field of the second antiferromagnetic layer by applying the first heat treatment at a heat treatment temperature of about 245xc2x0 C.
The exchange coupling magnetic field of the second antiferromagnetic layer can be also made to be about 1.58xc3x97104 A/m or more by applying the second heat treatment at a heat treatment temperature of about 270xc2x0 C.
In a more preferable composition ratio m ranges from about 49.5 to about 52.7 at %. Most preferably, the upper limit of m is about 51.2 at % or less. These composition ranges permit the exchange coupling magnetic field of the first antiferromagnetic layer at about 245xc2x0 C. to be larger, while making the difference between the exchange coupling magnetic fields of the first and second antiferromagnetic layers to be large, thereby enabling the directions of magnetization of the pinned magnetic layer and free magnetic layer to be readily controlled.
In another embodiment, the first and second antiferromagnetic layers are represented by PtmMn100-m-nZn, where Z is at least one element from the group of Pd, Ir, Rh, Ru and Os. The subscripts m and n represent the composition ratio and are preferably in the ranges of about 49 at %xe2x89xa6m+nxe2x89xa6about 53.5 at % and about 0.2 at %xe2x89xa6nxe2x89xa6about 40 at % and, more preferably, the range of m is about 49.5 at % to about 52.7 at % and, most preferably, the upper limit is about 51.2 at % or less.
It is preferred that n not be less than about 0.2 at % since the effect for improving the uniaxial exchange coupling magnetic field is not fully manifested. It is also preferred that the ratio n not exceed about 40 at % since the uniaxial exchange coupling magnetic field decreases.
In yet another embodiment, the first and second antiferromagnetic layers are represented by PtqMn100-q-jLj, where L is at least one element from the group of Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr. The subscripts q and j represent the composition ratios and are preferably in the ranges of about 49 at %xe2x89xa6q+jxe2x89xa6about 53.5 at % and about 0.2 at %xe2x89xa6jxe2x89xa6about 10 at % and, more preferably, the range of q is about 49.5 at % to about 52.7 at % and, most preferably, the upper limit is about 51.2 at % or less.
It is preferred that j be less than about 0.2 at % since the effect for improving the uniaxial exchange coupling magnetic field is not fully manifested. It is also preferred that the ratio j not exceed about 10 at % since the uniaxial exchange coupling magnetic field decreases.
The difference between the exchange coupling magnetic fields of the first and second antiferromagnetic layers may become more evident by allowing the composition of the first antiferromagnetic layer to be different from the composition of the second antiferromagnetic layer within the composition ranges as described above in the bottom type spin-valve type thin film magnetic element. This can be carried out by, for example, making the Mn concentration of the first antiferromagnetic layer to be larger than the Mn concentration in the second antiferromagnetic layer. As a result, magnetization of the free magnetic layer may be more certainly perpendicular to magnetization of the pinned magnetic layer after the second heat treatment. Many combinations for making the difference in the exchange coupling magnetic fields may be selected to improve the degree of freedom for designing the spin-valve type thin film magnetic element.